This invention relates to a method of dispensing discs or other flat objects and to a dispenser for carrying out such method. The invention is particularly, although not exclusively, concerned with a dispenser for the simultaneous transfer of a plurality of sensitivity discs, each impregnated with a different substance, for example various antibiotics, onto a flat surface formed by a thin layer of agar gel in a petri dish or similar container.
Such dispensers may be used in antibiotic susceptibility testing, the agar gel acting as a sterile nutrient medium for the organism being analysed. The organism is introduced onto the surface of the gel, and the discs are distributed over the surface of the gel by means of the dispenser. Each disc contains a different antibiotic, so that the effect on the organism of a plurality of different antibiotics can be simultaneously studied. The use of impregnated discs in this way is well known and will not be described further.
Several dispensers for the simultaneous dispensing of a plurality of discs are already known. The discs are generally stacked one on top of another in an elongate cylindrical cartridge. The discs are biassed to an exit end of the cartridge by means of an internal coil spring. Any one cartridge contains only discs impregnated with one particular antibiotic, details of which are displayed on the exterior of the cartridge.
Small hand dispensers can be made quite cheaply but generally suffer from the disadvantage that the positioning of the discs on the agar gel is not sufficiently precise for many purposes. The reason for this is that, in order to avoid undue force in applying each disc to the surface of the gel, most dispensers allow the discs to drop freely under gravity for a short distance onto the gel surface, this gravitational fall thus forming the final part of the transfer of the discs from their respective cartridges to the surface of the gel.
Other dispensers meet stringent disc positioning requirements, but fail because they apply the discs to the surface of the gel either with too much force, thus damaging the gel surface and burying the disc in the surface, or with differing forces as between different discs--some discs being pressed harder into the gel than others--and this immediately leads to non-comparable results as between the discs.